Formability and micromechanisms of DP600 dual phase steels in electric-pulse triggered energetic materials forming

Abstract

This paper investigates dual-phase (DP) steel’s formability and microscopic deformation mechanism under electric-pulse triggered energetic materials forming (ETEF). It provides experimental evidence and a detailed explanation for understanding the dynamic fracture mechanism and microstructure of ETEF. The present study analyzes the macroscopic fracture mechanism of ETEF specimens. Compared with quasi-static forming, the forming limits of ETEF with different strain paths (uniaxial tension, plane strain and biaxial tension) were significantly improved: the limit major strains were increased by 40.8 %, 78.2 %, and 18.2 %, respectively. Furthermore, SEM/EBSD/TEM observations revealed the relationship between the microstructure, kernel average misorientation (KAM), dislocation density, slip mechanism, and deformation twinning of DP600 steel. It was concluded that ETEF promoted the plastic flow of ferrite and martensite, reducing the void size and delaying the fracture failure of the material. High KAM increased the overall intensity of local grain deformation and reduced the strain gradient from grain interiors to grain boundaries. Under the condition of ETEF, a high fraction of low-angle grain boundaries (LAGBs) and refined grain size were obtained, and a high fraction of LAGBs enhanced the formability of DP steel. Additionally, {012}, {013} and {104} preferred planes appeared under ETEF conditions, forming a strong < 011 > preferred orientation and activating the slip mechanism of the < 100 > fiber component. Finally, TEM confirmed that coordinated deformation of the matrix led to improved formability of the DP600 material under ETEF conditions, as evidenced by the activation of the multi-slip system and deformation of the martensitic twins.